Production of hydrocyanic acid



Kleb., l?, Q.

E. {SUCHER PRODUCTION 0F' HYDROGYANIC ACID Filed July 7, 1923 PatentedFeb. 17, 1925.

nuire s'raras PATENT OFFICE.

QHN E. BCHER, F NEW YORK, N. Y., ASSIGOR- TO NITROGEN PRODUCTS COMPANY,

OF PEOV'DENCE, RHODE ISLAND, .A CORPORATION OF`BHODE ISLAND.

i PEODCTION O3? HYDROCYNIO ACID.

Application led July 7,

To all whom t ymay concern.'

Be it known that I, JOHN E. BUCHEN,

a citizen of the 'United States, residing at N ew York, in the county ofNew York and Siate of New York, have invented certain new andusefullmprovements in the Production of Hydrocyanic Acid, ot' whiclrtbefollowing is a specication.

This invention relates to the production of liydrocyanic acid fromcyanids or cyanid .containing materials which may be treated while in asolid state or in solution .to effect the liberation of hydrocyanicacid.

It has been stated by experimenters, that in the production ofliydrocyamc acid from cyanids or cyanid contamlng materials one 4ot twoconditions was necessary'in order to .t effect the formation ofhydrocyanic acid at a percentage yield-sufficiently approaching thetheoretical to malte the process practically operative and to preventpolymerization of the hydrocyauic acid, that is, that careful regulationof the reacting temperaw ture was .necessary in order to effect theformation of a relative large yield and the rapid .Withdrawal of thehydrocyanic acid from Contact with the reaction mass was essential inorder to' prevent polymerization of the hydrocyanic acid formed. These,conditions of operation necessitate careful manipulation ande'gulation,` and "require constant attention'to prevent temperaturevariations' as 'Well as means ade nate to maintain a constant and rapidWit drawal and vseparation of the .hydrocyanic acid formed.

' The main objects of the present invention are the production ofhydrocyanic acid from cyan'ids and cyanid containing materie als in asimple and etcient manner, Whereby a relative high yield may be obtainedand the resulting product be secured in such form and to such a degreeof purity as to render the same capable of utilization commerciallyeither as an article of manufacture or as the basis for theformation of cyanogen compounds, While avoiding the disadvantagesincident to the modes of op. eration as above described.

'Other objects and advantages ofthe invention relate to various novelmethods of operation as will be more fully set forth in the detaileddescription to follow.

In the carrying out of my 'improved process I may employ the cyanid orcyanid ,con-

1823. Serial No. 650,150.

taining materials in either solid form or as solutions, and I may usecyanid containing,r material such as that obtained from the fixation ofnitrogen by means of an alkali metal salt in the presence of carbon andironv as described in my U.l S. Patents 1,091,425

and 1,120,682.

My improved process comprehends in its broader aspects the formation ofhydrocyanic acid from cyanids or Venid containing materials by theaction or' organic acids or anhydrids, particularly carbon dioxid, as'lwell as some of tlieweaker inorganic acids such as sulphuro is acid. Al-

Although the action of c'arbondioxidl upon alkali metal cyanids in thepresence ot' moisture to form hydrocyanic acid has been known, muchtrouble has been ex er-ienced in the practical ellcctuation o4 thereaction by reason of the decomposition of thehydrocyanic acid eitherduring the process of 'formation or before it'could be separated in apure form. It is known that liydrocyanic acid in contact with suchsubstances as alkali metal cyanids ammonium cyanid, caustic soda, sodiumcarbonate, etc., polymerizes or ldecomposes and that., hence alkalinesubstances suoli as cyanids, carbonates, or liydroxids of potassiumsodium. or

ammonium greatly favor such decomposition or polymerization at ordinarytempera tures and are. more particularly active in promoting suchdecomposition at elevated temperatures.

'In order to overcome this diiiiculty it has been siigfesterl, that alarge excess of carbon dioxid be employed and that it .be passed throughthe cyanid or cyanid containing materials in the presence of moisturewith sufiicient rapidity to prevent poly-- merization. This-method offormation and sodium he usi' oyenid acid solution' of. very considerableirteihilit4 results even "ihen hut little excess of omelie ecid isbecause the aridity of (oxalic scid is so as comp-ered with that edcarbonio acid. [reid exalates of with similar results if desired. lli,on the other hund, one uses equivalent Quantities oit sodium cyanid andsodium bicarbonate to iii-erste hydrccysnic acid according -to theequation naouiinsiooseinQoogieneu there will he very'seriousdecimiposition when the nisse is ln like manner, sulphur dios'id,which is cheap end easily ohteined can he used in the seine iyay ascarbon dioxid, preferuhly keeping it or its Water solution in excess as'far as possible during the reaction. :it nray also he. used underpressure, and agitetion hy mcchunical means may he adviintageousiyemployed as in the case of carbon dioxid. Y

The hydrocyanic scid formed .may he removed 'from the solution or from.the'eztcess of acid gas employed by absorption in water either with orwithout agitation or in other Solvents in which the hydrocyanic reid isreadily soluble., rlhe hydrocyenic acid may he recovered ronrthe solventhyrectiication or it muy he conrcricd imo pero sodium cyanid oytreating` the solution withL sodium hydroxid. The solvent may he prescntWhen the hydrocyanic acid is liberated or the acid may he recovered froman aque- -ous solution hy agitating with benzene.

Another method of removing the hydro :yanie acid is hy .listillinn`under diminished pressure with a rectiiying column, so that the excessWater returns to the solution and' the gas passes throueh a dryingItower and vthen through a condenser, Whre' need he only inoderutelycooled, as there is no excessive amount of carbon dioxid present tolower th partial pressure of the -hydro cyanic ac id with consequentdifficulty in liqueaction'.

In fact, by certain olE the ahovfiwited methods the hydrocyunic acidwill beoh- `tained nearly or entirely free irom carbon dioxid or otherweak acid used as :i icuct ing' agent; and hence need he neither driednor condensed hut may he liqueicd or aspirated "directl through causticsoda to ohtain liquid hydocyanic acid or pure sodium cyanid.

In the case of the more stable solutions such-as will stend asuiiiciently high tem pcrature the acid may he r covered directly byboiling` and rectification Without the use ot diminished pressure.

As an alternative method ol removing,r the' hydrocyanie acid from thecontainer in which it is formed and te prevent undue ,contamination withcarbon dioxid gas l may sweep out the hydrocyenc acid by ineens ofcurrent oi' inert gus such es nitrogen. this Way the amount of carbondioxd 5. nich is mingled with the hydrocysnic acid Jformed is kept at aminimum end undue contamination' o the hydrocyanic :leid willi carbondioxid is prevented, there being normally only a sligjht amount oi cehon dioxid present in excess of that required to form the hydrocyanicacid when the process is carried out in the manner indictufud above.This is especially ad l'unizh geous where the exit is used to preparepure ,sodium cyanide i'romv caustic soda.

iiliy improved process comprchcnds the use of carbon dioxid. or otherrequivalent neuk acid ot' the character ahore. described. for reactingu'iou an alkali metal cyunid s0- iution, moistened cyuuid or cyunidcontaining material under conditions which serre to maintain thereactingl acid (as carbon dioxid) in excess of the cyauid or cyanidcontaining; material Wherchy the hydrocyanic acid liberated as n resultof the reaction is retained in the presence oi an acid nicdiu wherebypolymerization or decomposition oi' the livdiocyanic :wid formed isprevented regardless of the teinpcraturiJ 'so that the process can hecarried out cfiiciently at ordiimryY or room temperatures or eren higherit desired. 'By this method ot' operation the quantity of reacting acidcar-` bon dioxid) present in the hydrocyanic acid reduced lo a minimumsince thc reaction -chuniher onlr nccd contain l-livbrcucting acid inexcess. he gases from the reaction chamber may he passed through watermrother ii uid in which the reacting gas is less readily soluble than thehydrocyanic yacid 'formed to absorb the hydrocjanic acid "which may berecovered from the water 0r solvent hy means oi a fractionatiwr columnoperated either with or without c iminished pressure. If desired u smallquantity of strong ucidinay he added to such solvent in order tosta-rise the hydrocyanic acid. The relatively small amount of carbondioxid or other reacting' gas passes over Without inatnrinl ,absorptionin the solvent. It is re garded as prefer-.dile thir [he cyunid orcyanid containingT material be agitated whilein the rcuction zone tohasten the reaction end supcratmosphcri'c Apressure may 'he employed toad 'nntage as promotingrY the reaction.

' In the. accompariying drawings is shown forms or" apparatus which mayhe employed in carrying out my improved process alhough it is to heunderstood that the upparatus shown is illustrative only, und vthatother iorms and arrangements of apparatus may be employed for thepurpose or the structures snmrn may he varied greatly Without departingfrom the essential? features of my invention.

Fig. l is a-diagremmatic illustration of y solutions to a forni ofapparatus which may be employed in the recovery of hydrocyanic 'acid'from solid cyanid bearing material by myv improved method, and,

Fig. '2 is a view which may be employed for treating cyanid convert theycyanid tohydrocyanic acid' by my process.

spout #1 communicates with lthe base of the" chamberl 1 and may beinclined somewhat as :with the reaction charge pipe 32 'whereby thereacting acid b isz-brought into thorough contact lwith the shown iiiFig. 1 to provide a passage forz the material. i ed in the 'spout lland.comprises a shaft@ Asupported by bearings 7 and Sand driven in anysuitable` manner from a gear 9.. ,The spout at is provided With anenlarged poi'- tion 10v With which a pipe 11 communicates whereby thematerial may be sprayed With a sufficient amount ot' water to meistenlthe material so will be present to secure complete orsubstantiallyc'omplete conversion of the cyanid to hydrocyanic acid..Thelo'xv ot Water in'V the ipe 11 maybe suitably controlled b vregulating the valve 12.

The lower end ot the spout 4 communicates with a reaction chamber 14 ofsuitable size which receives the material from 'the spout 4.- and whichis nominally filled with the 'Weak reacting acid in vapor forni,sucli,\-for example, as carbon dioxid. 'lhe lcarbon dioxid is suppliedtothe reaction chamber 14; by a pump 15 which forces the carbon dioxidthrough a pipe 16 and a ytrap'd', -from' which it passes to the reactionchamber through a -Wit-h a .valve lf). The pipe 18 communicates chamberthrough the discyanid containing material. A pipe 20 coniy inunicateswith the spout li, a short distance above the point Where it enters thereaction chamber 14, and passes to a solvent containing tank '22. Thepipe 20 is providedi'vith a `valve 21 the use of which Will be referredto more particularly. hereinafter. l'Ig'ie tank 22 is part-iallylilledwith a suita l than carbon dioxid or vthe other Weak acid employed forcarrying out the reaction.

otone form of apparatus.

as briquets orv .powdered material containing an alkali' fixation. ofni- A screw conveyor 5 is mount-v hydrocyanic acid termed as reactionand alternately cut olf. from thev that anproper amount ot' Water pipepipe 18 provided solvent 23 such as Water, etc., in whichv hy roc'ya'nicacid is more readily soluble 2l provided with a valve 25 through which ithe carbon dioxid or 'other reacting acid which is not absorbed by thesolvent may be drawn eti". Pressure in the tank 22fmay suitable .periodsby' means be reduced at apparatus 28 whereby the oft a vacuumhydrocyanic acidV taken up bythe solvent I may be removed' and drawn olithrough pipe Lf order h,'drocyanic acid, such, forexample, as by heini;passed through a drier, condenser, etc., to remove moisture andeliminate traces of the' reacting acid which may 'be contained therein.The tank 22 may be' suitably cooled to increase the Iabsorption of vthehydrocyariic acid While' the reacting acid to be treated in any desiredmanner in to complete the purificationv of the I gas passes over andescapes throughthe pipe 24'. A drain pipe 30 is provided by which thesolvent liquid may beremoved from the tank when desired. ln operationtwo or more tanks 22 lmay be employed and these may be alternatelyplaced in communication with the reaction chamber toabsorb reactionchamber to operate the vacuum-apparatus and remove from the' liquid 'thehydrocyai'iic acidV previously absorbed". The valve 2l is provided forthe pnrposeof permitting:r each tank to be disconnected frein thevreaction chamber wheneverdesircd. 'A discharge' 4cylinder 32 co'nimuiiitetes with ber und contains a screw conveyor 33 operated by gears 34:for withdrawing the treated material lfrom the reaction chamber afterthe conversion of the cyanid contained therein to hydrocyanic acid.v

A pipe 35 extends downwardly froni the 32 for the passagc'oit' theconverted cyanid bearing material, and is provided with a valve 36 whichmay be closed while the reaction is proceeding to prevent escape' otthcreacting gas but which may be opened' at suitable intervals and theconveyor 33- traverses the spout .pump 15 and caused to traverse thereac-l tion chamber' L1 in sulicient quantity to maintain an excess olacid in the reaction the 4base or' tlie reaction cliani' the materialfrom the a result, of the material is fed into the reaction chamberthrough the spoutjl the material is stirred or agitatedby the movementof the conf,

veyor 5 as the carbon dioaid or other acid contacts therewith which alsotends to hasten the reaction. During the operation the valves 36 and 21maybe closed to prevent escape of the gases and 'permit the desireddegree of superatmosi mova'l ofthe gases 1 ber to prevent unduecontamination with the A being suitably pheric pressure beinO maintainedin the reaction chamber. llhen the process has been continuedsuificiently to form the desired amount of hydrocyauie acid in thereaction chanber the flow of cyanid containing material may be stoppedand the valve 21 opened 'and the gases allouedto pass through the pipe20 and into contact with the solven'L 'in the tank 22. The tank 22cooled and the hydrocyanic acid being readily soluble -in lthe solventit will be taken up readily and the reacting acid gas Which-is sparinglysoluble in the solvent used may pass over and be Withdrawn through thepipe 24 'Where it may be treated to remove the small quantities ofhydrocyanic acid carried over therewith. The valve 19 `may be closedduring the re- 'rom the reaction chamreacting acid gas. When the solventin the tenir 32 has absorbed as much hydrocyamc 10i-acid as it willreadily contain under the conditions prevailingthe valves 21 and 25 maybe closed and the vacuum apparatus 28 operated to reduce the pressureupon the tank 22, the temperature oii'which may also be raised ifdesired to further facilitate the removal of the hydrocyanic acidcontained in the solvent. After the removal of the hydrocyanic acid gasJfrom the solvent in the tank 22 it may be passed through driers andcoudciisers to remove the slight amounts of water vapor and reactingacid contained therein when it may bc con'ipressed or caused to reactwith an alkali metal hydroxid to produce pure alkali metal c anid.A'ttcr the gases have been substantially removed vfrom the reactionchamber thevalve 36- maybe opened and the conveyor 323 operated toremove the spent material and prepare the reaction chamber for thetreatment of afresh supply of cyanide material. l

If preferred, the method of removing the hydrocyanic acid 'from thereaction cham ber may be modified by alternately passing the lgases fromthe reaction chamber into the portion of any one of a plurality of tanks22 whereby there is less interference with the hydrocyanic acid formingreaction inthe reaction chamber and the process can be operatedsubstantially continuously. It is to be understood that various changesmay be made in the apparatus and the same may be modified to conformlwith changed conditions which may arise in practice While the method oftreating the gases with a suitable solvent may be varied Withinreasonable limits without departing trom the spirit and scopeof thepresent inventionn The form of apparatus shown in Fig. 2 of the drawingsis more particularly adapted for carryingl out the reaction with asolution oi alkali metal cyanid and comprises a eyanid containing'receptacle having a pipe 30 communicating with the reaction chamber 2li'and having a valve 38 therein for regulating the flow of the cyanidcontaining solution. A pump') is provided ior passing carbon dioxid orother suitable weak acid through `the pipe Ll0, trap 41 and pipe 42 tothe reaction chamber. The reaction chamber may be partially filled witha suitable liquid such as .vatcr and provided with a stirrcr 44 carr'iedby' a shaft l5 and operated b v gears i6 from a shaft 47. A pipe 48leads from the reaction chamber 37 to a. vacuum pump 49'. the pipe beingprovided with a valve 50 and vacuum gauge 5l. A pipe 553 leads from thevacuum pump to suitable driers and rondensers (not shown) for thereception and purification of the hvdrocyanic acid. and the reactionchamber 3T is provided with a drain pipe 5a having a valve therein.

In carrying out the process by means of the apparatus shown in Fig. thecyanid containing solution is placed in the container 35 and the "valve3S adjusted to permit a proper amount of the material to flow into thereaction chamber. 'lhe reaction chamber is partially filled with wateror 1 other solvent and carbon dioxid or other suitable reacting gasadmitted to the reaction chamber by opening the valve 56 in the pipe 42and starting the pump 39. The space above the liquid in the reactionchamber is filled with carbon (li'oxid or other reactive acid and thisacid is constantly maintained in excess to prevent substantialpolymerization o1 the hydroeyanic acid formed. The reactive acid may beforced into and maintained in the reaction chamber underthe desireddegree of super-atmospheric pressure and thc liquid may be agitated bymeans of the stirrer 44. When a suflicient ruantity of l'iydrocyanicacid has been ormed to reduce a high degree of concentration' in thesolvent in the reaction chamber the valves 38 and 55 are closed. thevalve 5v() opened and the pump 49 started to remove the bydrocyaniclacid from the 1 carbon 'dioxid `or other v pressure,

vso

; nitrogen fixation The-'term weak acid as employed hereiny into a'reaction chamber Mtity of weak acid .which p in' proportion to y smallquantity into a` reaction. chamber maintained under fsuperatmosplie'ric,pressure and containing acid .inl excess of thel solvent; ln thiscasesniveteifrtisili,v sliepen-ijf reactive gas zo be mixedv i lil therecovered 'hydrocyzinic acid is .that 'Winch 'lls the space chamberabovefthe 'solvent' and such 'slight 'amount asmay be 'taken up bythesolyen and `removed therefrom underv diminished which hydr'ocyanicacid is much more rendily soluble than, is' the reactive acid;

cyanw. containmg material asA employed in pended claims 'is' employedgeneric either in solid former as a'solntion as well as suchv cyanidcontaining material tained'A from the formation of cyanide in processesgenerally. is intended to embrace the anliydrides men*- tioned such 'ascarbon dloxid. and sulphur 'd10X1d,'tliese .substances being nsed in thepresence of water which 1s tion.

What l claim is c p L'The process 'of producing liydrocyanicifeedinzggf4 a relatiieljy` small quantity of cyanid containing inaerialcontaining a einen-v is relatively large elle quantity of cyanidcontalnlngmaterisl contained in the chamber `which has not been actedupon' by the acid, whereby an excess 'of 'said Weak acid is maintainedin the reaction chamber sui cient to prevent polymerization oi the liy"dlfocyan'ic acid formed.

` l heprccess of producing hydroeyanic acid from vcyanid containingmaterial, which comprises, 'continuonsljfv feeding' a relatively ofcyanid containing maierial :1 quantity of Weak quantity of 'cyamdcontaining .n'iai-e.'-ial .in

. the `fiction chamber Wliiclilias not been "material with waier whilemaintaining an excess oi'said. weakncid 1n the reaction zone to preventanic acted upon by the acid. i

3. The process of producing' liydrccyanic acid from cyanid containingmaterial which comprises treating' the oyaniil con'eaining o weak acidin the presence of substantial polymerization of the liydrocy acid.formed,-and absorbing 'the hydrocyanic acid forined as a result of the.read .tion in a mediurnin which the Weak acid is 'of water and agiieiingthe less soluble than 'the hydrocyanic acid.

.4. The process of producing iiyd'rocyanic material which comprises.treating material' with a weak aci in the presence in the reaction theAsolvencselected' being one in' as is olo- I necessary inthe ycarrymgoucof the ilydrocyanic acid renc from cyanidiconta-iningrnaieriai which.

material While4 maintaining @fiile ieeiiii: cient io prei/enomissioni-ini of the iiydrocyanic acid '5. Tlie process prodncing lig/dacid from cyiiid conai" comprises tre-sting the materiel with n Weak@serial which While agitsiing the reaciiive Ytanning' an excess oritheir@ 4to prevent snbsten'iial peiyn,

hydrocyanic acid formed. dTlie process of 'producir acid from cyanidcontaining in comprises treating; lie c material with a Weak ec waterand agitaiing ri-.lie i active mass Wliiie maintaining an excess oii thenealr'acid in cient aierial which nid containing polynieriization pgenio 'in rfi-nid @remaining in presenceoi" waiter and .undersnpcraniosplieric presslnfeA and mainal'cill 1 the presence oiviiydrocyonie the 'reaction none7 absorbing' the liydro.-

cranio acid formed y tion in a inedinin in W ille Wealra'cid is lesssoluble than lie iiyi'irocyunic ecid. l 7. The process of producingiiydrocyenic scid from cyanid containinggro 'wir comprises treating lieoren l coni-aining niajteriai fir/ith a Week acid in lie ifviesence ofnexter and under siiperaimomlier'ie precisare, and" absorbing the hydroceci formed as a resnli, of the reaction c i Y'fedinm in Wiiicli thewealracid less sol liydrocjfanic scidn 8. The process of prodncin acidfrom cyanid Contarini? i comprises' treating elle c., inoie'rialwitli aWeak acid 'in i p .ne presen-ee water While maintaining an excess ofseid Weak acid in the neectifmy sione no sulist'aniial polymerization cilie iiydrocyformed. absoroing'tlie iiji'drocy anic acid p A i Aacidin amedium in Y'which the-Weak scid is less solnbie than'tlie liydrocvanicacid,

sepaiaiaing the liydrocyanc d from elio solvent nnder reduced pres5%.3'l`i1e process of prodi acid from c vanid containino comprisestreating the c'jfanic tei'inl with .awealraeid in water and ngtating theinainaining an excess oi' ne vreaciion' zone, absorbingr t acid4 formedesa result of fic r rnedinni 'in which the 4weak s c oie than thehydrocyanic acid. ing 'the hydi'ocyanic acid "from iii@ under reducedpressure, ik

10.. The process oi producingliydrocjfaniu acid from cyenid containingmaterial which comprises treating the c vanid containino' materiel witha Weak acid in the presence or Wateraiid onder snperati'no splierpressure, -absorbinggltheliydrooj ,nic acid formed as a result o'i thereaction in a medium in which the Weak lacid. is less cyanic acid, endseparating elle lfiydrccyanic meid from tire solvent under a pressureless n drocyanic .serial Winch amine," 'ine a result 0:5 islie reac# Cile than the Hifi...

soluble than lie liydrothan that at which the absorption of the hy'-drocyanic acid in the solvent was effected.

11. The process of producing hydrocyanic' acid from cyanid containingmaterial which comprises treating the cyanid containing material withcarbon dioxid in the presence of water and agitating thereactivc masswhile maintaining anexcess of carbon dioxid inthe reaction zonesufiicient to prevent substantial polymerization of the hydrocyv'anicacid'but relatively small in proportion to the hydrocyanic acid formedas a result of the reaction.

12. The process of producing hydrocyanic acid from cyanid containingmaterial which comprises treating the cyanid containing material withcarbon dioxid in the presence of water and under superatrnosphericpressure while agitating the reactive mass.

' 13. The process of producing hydrocyanic acid from cyanid containingmaterial which comprises treating the cyanid containing material Withcarbon dioxid in the presence o-Water While maintainingr an excess ofsaid carbon dioxid in the reaction zone to prevent substantialpolymerization of the hydrocyanic' acid formed, and absorbing thehydrocyanicacid formed as a result of the reaction in amediurn in whichthe carbon dioxid is relatively less soluble than the hydrocyanic acid.

14. The process of producing hydrocyanic acid from cyanid containingmaterial which comprises treating the cyanid containing material withcarbon dioxid in the presence of Water While agitating the reactivc massand maintaining an excess of carbon dioxid sufficient to preventsubstantial polvmerization of the hydrocyanic acid formed.

The process of producing lrvdrocyanic acid from cyanid containingmaterial which comprises treating the cyanid containing material withcarbon dioxid in the" presence of water and under superatmosphericrpressure while agitating the reactive mass and maintaining an excess ofthe carbon dioxid Y, sufiicient to prevent substantial polvmeriza- -tionof the hydrocyanic acid formed.

16. The process of producing hydrocyanic acid from cyanid containingmaterial which comprises treating the,cyanid containing material withcarbon dioxidl in the presence ,of .water and agitating the reactive'mass while maintaining an excess of the carbon dioxid in the reactionzone," and absorbing the hydrocyanic acid formed as a result of thereact-ion in a medium in Which the c'arbon dioxid is soluble to a lessdegree than the hydrocyanic acid.

formed as a result of the reaction in av medium in which the carbondioxid is less readilisoluble than the hydrocyanic acid.

18. The process of producing hydrocyanic acid from cyanidcontainingmaterial which comprises treating the cyanid containingymaterial with carbon dioxid in the presence of Water While maintainingan excess of carbon dioxid in the reaction zone to prevent substantialpolymerization of the hydrocyanic acid formed, absorbing thehydrocy'anic acid in a medium in which tli'e carbon dioxid is lesssoluble than the hydro'- c vanic acid, and separating the liydrocyanicacid from the solvent under reduced pressure.

19. The process of producing hydrocyanic acid 'from cyanid containingmaterial which comprises treating the cyanid containing material withcarbon dioxidin the presence of water and agitating the reactive masswhile maintaining an excess of the carbon dioxid in the reactionzone,absorbingtlie h vdrocyanic acid formed as a result of the reactionin a medium in which the carbon dioxid is less soluble than thehydrocyanic acid` `and separating the hyrdocyanic acid from the solventunder reduced pressure.

20. The process of producing hydrocyanic acid from c vanid containingmaterial which comprises treating the cyanid containing material withcarbon dioxid in the presence of water and under superatmospheric pressure. absorbing the hydrocyanic acid formed as a. result of the reactionin a medium in which the carbon dioxid is less soluble than thehydrocyanic acid, and separating the hydrocyanic acid from the solventunderv a pressure less than that at which the Aabsorption of thehydrocyanic acid in the solvent was e'ectedl 21. The process ofproducing hydrocyanic acid from cyanid containing material .whichcomprises treating the cyanid containing material with carbon dioxid inthe presence of water and agitating the reactive mass'`- whilemaintaining an excess of carbon dioxid in .the reaction zone suliicientto prevent substantial polymerization of the hydro'cyanic 'acid formed,and removin the. hydrocyanic acid from the mass wit out materialcontamination by the carbon dioxid. ,V

'."In testimony. whereof I have axed my signature; 17. The process ofproducinghydro'cyanic A `Joran E; BUCHERL'

